<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>菜鸟教程(runoob.com)</title> 
</head>
<body>

<p>回调函数等待 3 秒后执行。</p>
<p id="demo"></p>
<script>
// setTimeout(function () {
//     document.getElementById("demo").innerHTML="RUNOOB!";
// }, 3000);
setTimeout(function (){
    document.getElementById("demo").innerHTML = "Javascript"
},3000);
</script>

</body>
</html>